This invention is generally directed to improved cold pressure fixable toner compositions, and more specifically the present invention is directed to single component pressure fixable encapsulated toners containing as a core component magnetite encapsulated by a polymeric shell prepared by interfacial polymerization. In one embodiment of the present invention there is provided a single component pressure fixable magnetic toner composition containing as a core a mixture of magnetite, and certain copolymer compositions, admixed with an organic solvent. This core is encapsulated with a pressure rupturable polymeric shell generated by interfacial polycondensation in an aqueous dispersion of reactants, wherein the surface of the magnetite core particles can be modified by chemical reaction with various stearates, including ammonium stearate, for the primary purpose of obtaining a desirable high concentration of well dispersed magnetite particles in the final toner composition. The toner compositions of the present invention are useful for causing the development of images in electrostatographic imaging systems, particularly electrostatic imaging systems wherein pressure fixing, especially pressure fixing without the presence of heat is selected.
The development of images, and in particular electrostatic images utilizing developer compositions containing toner materials is well known. In many of these systems an electrostatic latent image is formed on a photoconductor member, and the image is developed with a toner composition comprised of resin particles and carbon black. Subsequently the developed image is transferred to a suitable substrate wherein fixing is accomplished by heat. Accordingly final copies of the toner image are produced by heating the toner to a temperature at which it begins to flow enabling fusing of the particles to a support substrate such as paper. This fixing process generally requires substantial amounts of energy, and prior to producing the first copy in an apparatus with a heat pressure fixing system an appropriate temperature must be achieved for proper fusing. Other similar fixing systems are known including radiant, vapor, pressure, and combinations thereof.
Cold pressure fusing, also known, has a number of advantages primarily relating to the requirement for less energy, since the toner compositions involved can be fixed at room temperature. Nevertheless, many toner compositions used in prior art cold pressure fixing systems suffer from a number of deficiences. For example, these toner compositions must usually be fused under high pressure, and these pressures have a tendency to severely disrupt the toner fusing characteristics of the compositions selected. This results in images of low resolution or no images whatsoever. Also, in some of these systems substantial image smearing has been noticed in view of the high pressures required. While attempts have been made to improve toner compositions for cold pressure fix systems, these compositions in many instances have a number of undesirable characteristics, including agglomeration of particles at room temperature, insufficient flowability under high pressures, lack of adhesion to the support substrate such as paper, unsuitable blocking temperatures, and an insufficient brittleness to allow the preparation of such materials by, for example, known commerical jetting methods, or known fluid energy milling processes. Additionally, the cold pressure fixing toner compositions of the prior art have other disadvantages in that these comositions when used for development result in images with high gloss that are of low crease resistance and undesirable low smear resistance. Further the resulting images undesirably inhibit carbon-paper effect, that is there is a total or partial image transfer from the imaged substrate to neighboring substrates caused by pressures arising from normal handling. In some situations these disadvantage can be substantially eliminated by the use of certain coated papers. In contrast, images developed with the pressure fixable single component toner compositions of the present invention have a matte appearance on plain paper, are of high smear and crease resistance, and further there is substantially no carbon paper effect observed.
There is disclosed in U.S. Pat. No. 4,307,169, microcapsular electrostatic marking particles containing a pressure flexible core and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polycondensation in an aqueous dispersion of reactants on and about the core. According to the disclosure of this patent, reference column 2 beginning at line 10, the microcapsular electrostatic marking particles are comprised of colored encapsulated pressure fixable substances contained within a pressure rupturable shell, and a residue thereover. Specifically, the ink selected for the toner composition of the U.S. Pat. No. 4,307,169 includes organic or inorganic pigments, magnetite, or ferrites, or other magnetizable substances, while the carrier medium for the ink may comprise a solvent or a plasticizer including for instance dibutylphthalate. The polyamide shell of the U.S. Pat. No. 4,307,169 is prepared by an interfacial polycondensation process. While the pressure fixable magnetic dry toner composition of the present invention is similar to that composition as described in the U.S. Pat. No. 4,307,169, it differs in a number of significant characteristics including, for example the user of a polymer in the core, which polymer is different in its composition and properties than the polymer selected for use in the U.S. Pat. No. 4,307,169. Thus, the polymer selected for the core of the present invention is a triblock polymer comprised of a polybutadiene segment, for example situated between two polystyrene segments. Accordingly, the morphology of this polymer is significantly different in its structure and properties than those materials disclosed in the U.S. Pat. No. 4,307,169, enabling the triblock polymer of the present invention to absorb and retain substantial amounts of low molecular weight additives, such as oils without phase separation under atmospheric pressure. Additionally, the polymers of the present invention enable the absorbed oil to be fully or partially desirably released under high pressure, the extent of this release being dependent for example on the pressure applied to the shell, the molecular weight of the triblock polymer, the ratio of styrene to butadiene in the polymer, and the molecular weight of the oils selected. Therefore, in xerographic imaging processes the released oil will assist in causing the polymer to penetrate and adhere to the paper substrate. Moreover, the unique morphology if the triblock polymer enables the production of desirable matte images.
Further there is disclosed in U.S. Pat. No. 4,407,922, pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of polymers of polystryene-co-stearylmethylacrylate as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component, and a polyisobutylmethacrylate composition as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component, wherein the soft component is present in an amount of from about 35 percent by weight to about 75 percent by weight, and the hard component is present in an amount of from about 25 percent by weight to about 65 percent by weight.
There thus continues to be a need for improved toner compositions, particularly dry toner compositions for use in imaging systems wherein cold pressure fixing processes are selected. More specifically there remains a need for single component cold pressure fixable dry toner compositions which exhibit excellent flowability at selected pressures, adhere to the substrate on which the image is to be permanently fixed, and wherein excellent images of high resolution result. Moreover there continues to be a need for improved encapsulated single component toner compositions wherein the image subsequent to fusing has a matte finish. Furthermore there continues to be a need for dry single component toner compositions wherein the shell can be prepared by interfacial polymerization processes. Also there continues to be a need for dry single component magnetic encapsulated toner compositions which possess desirable functional mechanical properties. Furthermore there continues to be a need for colored single component pressure fixable magnetic toner compositions wherein the magnetite particles are replaced with selected pigments including magenta, cyan, yellow, and the like. Also there is a need for encapsulated dry single component toner compositions which possess in combination excellent fixing characteristics, allow matte or nonglossy images with no carbon paper effect. Additionally there continues to be a need for encapsulated dry single component toner compositions which allow crease resistant images to be formed.